Fix issues with PopupHelpWidget on Linux and macOS

* Clean up parent alignment code
* Don't hide widget if it currently has focus
* Use Qt::Tool window type on macOS as well. This prevents the popup help from hiding to the background if the main window has focus.
* Fixes #2814

src/gui/SearchWidget.cpp

@@ -38,7 +38,6 @@ SearchWidget::SearchWidget(QWidget* parent)
     setFocusProxy(m_ui->searchEdit);
 
     m_helpWidget = new PopupHelpWidget(m_ui->searchEdit);
-    m_helpWidget->setOffset(QPoint(0, 1));
     Ui::SearchHelpWidget helpUi;
     helpUi.setupUi(m_helpWidget);